It is well known that plastic containers can be produced from preforms in a stretch blow molding process.
Alternatively to inflating the containers with compressed air, EP 1529620 B1 describes a method of hydraulically shaping preforms into plastic bottles. To this end, the preforms are first heated and then transferred to a hollow mold where they are stretched in a longitudinal direction. In addition, mineral water or the like is introduced under excess pressure so as to establish the final container shape. The mineral water remains in the container, so that a subsequent separate filling step can be dispensed with.
US 2011/0031659 A1 additionally describes a method comprising the steps of stretching a heated preform by means of a stretching rod and expanding it then hydraulically by means of an incompressible fluid, in particular water, so as to form a container. Subsequently, the fluid is displaced by means of compressed air and exits the container.
When a stretching rod is also used for filling in the product or when a filler neck is introduced in the container for the purpose of filling, they displace a certain volume in the filled-in product. It follows that, when the stretching rod or the filler neck are removed from the container at the end of the filling process, the filling level will drop. In addition to the fact that the final filling level deviates from the desired filling level, also the ullage is larger than desired, since, with the stretching rod or the filler neck inserted, a smaller amount of filled-in product will already suffice to reach a maximum admissible filling level. Hence, the problem arises that the final filling level of the liquid product may vary, and especially that it may be lower than the desired filling level.